
Parting 



Gold and Silver by 

Iron at Lautenthal. 

>/ 

% BY T. EGLESTON, Ph.D. 


* 1 

l may ii mi) 

, J 


■:V ; , G 





& \ x S- - ~y i i, ’ • 


YV - VrGv • . 




Means of . 










• v 

















PLAN OE 
THE 

GOLD PARTING 
WORKS 

AT 

^4 


SCALE l;80 

j-1-1- l -—l-» • » 1 - — - - - i 

12345678 9 10 METERS 

== ____________________ ========== __RUSSELL & SRUTHERS, 


ENG’S.N.Y. 





























































































































































































































































Reprint from School of Mines Quarterly. March. 1885. 

— . */ * ; ' ’ ' > 

.1 



|A V< 


'.s'- 


t 



PARTING GOLD AND SILVER BY MEANS GF IRON 

• AT LAUTENTHAL. 

BY T. EGLESTON, Ph.D. 

Having had occasion in the year 1882 to visit the works at 
Lautenthal, in the Hartz Mountains, where the silver and gold, 
which are produced in the Hartz, are parted, I have thought it 
would be of interest to describe them, as the process is exceed¬ 
ingly interesting and the plant a very simple one. At the time 
of my visit they were regularly parting 1500 kilos of silver 
bullion per. week, which contained quite a large quantity of gold, 
the proportion being variable according to the quantity of ores 
from this country which were purchased for treatment. The 
works are situated in a building used only for that purpose, 

which is divided into three rooms. In the first of these the solu- 

... . • ** * ■ 

tion and precipitation are effected. In the second the mother 
liquors are treated; in the third the gold and silver produced are 
prepared for market. The legend below gives the full descrip¬ 
tion of this plan. 1 

A and B. Cast iron solution pots. 

C. Lead vat for weak acid solution. 


1. In the year 1880 I translated an article by B. Rosing for the Director of the U. 
S. Mint, to whom I am indebted for the use of the plates made for that article. I 
have also freely used the information contained in it either to supplement or con¬ 
firm my own notes taken in the works at Lautenthal. 




D. Lead steam vat for treating the liquors from R. 

d. Launder for draining N and S. 

e. Chimney vent for the escape of the acid fumes from A 

and B. 

f. Space covered with lead for the settlings from the vat D 
and the tank N. 

g. Launder for carrying off the liquid from H. 

H. Wooden vat lined with lead for treating the silver sul¬ 
phates. 

i. Chimney vent for carrying off the acid fumes from P. 

K. Wooden tank lined with lead for the wash waters contain- 
ing gold and silver. 

k. Launder with partitions for settling the liquors from H. 

M. Copper vessel for cleaning the silver sulphate. . 

N. Vats for crystallizing the iron sulphate. 

o. Steam pipe for heating the liquors in T. 

P. Cast-iron pot for treating the gold residues. 

p. Injector for raising the liquors from R into D. 

Q. Iron boiler for heating water. 

R. Basin for settling the liquors from H and K. 

S. Vat lined with lead for draining the iron-sulphate crystals. 

T. Lead vat for treating the insoluble residues from A and B. 

U. Muffle for driving the water out of the silver cake. 

u. Sheet iron chimney of the muffle. 

V. Furnace for melting the silver. 

v. Place in the vat H to which the silver sulphate is drawn. 

W. Furnace for melting the gold. 

X. Heated cast iron plate on which the silver is cast. 

Y. Table for the hydraulic press. 

Z. Bin for silver slags and rich residues, 
z. Bin for broken crucibles. 

The process is composed of five different operations. 

1. Solution of the silver in sulphuric acid. 

2. Reduction of the silver sulphate by means of iron. 

3. Purifying the silver and melting it into ingots. 

4. Treatment of the sulphuric liquors. 

5. Purifying the gold and melting it into ingots. 

I. Solution of the Silver in Sulphuric Acid. 

The metal is first inquartated and granulated. It is then 
placed in one of the cast-iron kettles, A or B, arranged as shown 


3 


in Plate I, Fig. i. The bottoms of the kettles, which are some¬ 
what thicker than the sides, are heated directly by the fire. The 
ash pit is very much inclined and is connected with the vat, S, 
Plate 2, Fig. 2, set in the floor of the works to catch the contents 
of the pot when it breaks. The charge is from 400 to 500 kilos 
of silver, which is the usual work for a day. This is treated 
with twice its weigh of sulphuric acid at 66° B. The charge is 
placed in the pots in the evening. If it is to be 400 kilos, which 
is the usual charge, 600 kilos of the strong acid, which has been# 
used to treat the gold residues, diluted to its proper gravity with 
200 kilos of the weak acid from the pot C, shown in Plate 1, is put 
poured over it and left until the next morning. Only 0.9 part of 
acid are required to dissolve the silver, but it is necessary that the 
silver should not only be dissolved, but that the silver sulphate 
should remain in solution, so that a great excess of acid must be 
used. This has no inconvenience unless the acid is made too 
dilute, in which case the iron of the pots is attacked and the 
residues make the gold residues impure. The use of dilute 
acids also somewhat lengthens the process. The pots are 
covered with a cast-iron cover which fits tight. In this, a lead 
pipe is fitted, which enters the flue at c , and carries off the 
sulphurous vapors. The silver is left over night with the acid on 
it. In the morning a fire is kindled under the pots. A gentle 
fire is kept up in order to prevent the too energetic boiling 
of the acid. If for any reason it commences to foam, the acid 
must be cooled down. This is generally done with the acid 
taken from the pot C. The sulphuric acid attacks the silver and 
dissolves it. The reaction which takes place is represented by 
the formula 

2 AgT 2 Fl 2 S 04 = Ag 2 S 04 TS 02 T 2 H 20 . 

Any particles of the silver sulphate which may be carried 
off in the vaporized acid are for the most part caught in the soot 
in which the acid condenses. When the flues are cleaned the 
soot is washed in the wash-kettle, M, and most of the silver sul¬ 
phate recovered. When most of the metal is dissolved, which 
takes from ten to twelve hours, the hot liquor is ladled out with 
copper ladles 0.18 in. in diameter and o. 10 111. deep, into a lead- 
lined vat, and poured from thence into the second vessel, B, 
where it is mixed either with water or the weak solution from 
the succeeding processes, or both, until it is at 6o° B, and is al- 


4 


lowed to remain there for two hours. The weakening and cool¬ 
ing of the solution causes the silver sulphate to crystallize out in 
the bottom, of the vessel. When this is complete, which can be 
easily seen, the supernatant weak acid is ladled out to the lead- 
lined vat, C, and is again used from there to mix with the 
stronger acid. 

The solution in the pot, A ,is made twice; the accumulating gold 
residue is then treated. At first the silver solution was trans¬ 
ferred immediately from A to //, and then allowed to crystallize, 
but this practice had to be abandoned, for the very large amount 
of free acid contained in the sulphate, produced with the iron 
such very large quantities of hydrogen, that not only were the 
workmen driven out of the works by it, but very perceptible 
quantities of silver were lost. By the method now used, most 
of the free acid is separated before the silver sulphate is trans¬ 
ferred, and this inconvenience no longer exists. 

II. Reduction of the Silver Sulphate by Means of 

Iron. 

The mass of yellowish crystals of silver sulphate in the bot¬ 
tom of the pot B , freed as much as possible from acid, are trans¬ 
ferred with ladles into cylindrical copper vessels 0.32 in. in diam¬ 
eter and 0.30 in. deep, to be treated in the lead-lined vat, H. 
There are two of these tanks together, //and K, Plate 1 and Fig. 
3, Plate 2. They are exactly alike, being 2.70 in. long by 1.10 
in. wide and 0.55 in. deep. The lead is turned over the top of 
the sides, which are 0.25 in. thick. The bottom of each is inclined, 
being o. 10 in. lower in the central than at the opposite end. 

The silver sulphate placed on the bottom is covered with wa¬ 
ter, and pieces of very thin and pure scrap iron, the residue from 
the manufacture of buttons, are then placed in it. The sul¬ 
phuric acid goes to the iron and forms iron sulphate, while the 
silver becomes metallic. The iron is added very gradually, care 
being taken not to make a fresh addition before that previously 
put in has been dissolved. During the whole time that the iron 
is being added, the material in the vat must be carefully stirred 
with the wooden stirrers, Fig. 4, in order to break up any lumps 
of silver sulphate, and to bring the iron into intimate contact with 
it. Towards the close, when nearly all of the sulphate is re¬ 
duced to silver, the iron must be added with great care, so as 


5 


not to have an excess of it. Towards the last the strips are 
hung in, so as to be certain not to have an excess of iron, which 
would make the silver impure and increase the quantity of slag 
in the melting, and consequently the loss. In order to ascertain 
when the whole of the silver sulphate has been reduced, the 
solution is tested with a strip of copper or a solution of salt. 

If for any reason there is an excess of iron, a little copper 
sulphate is added, which throws the copper down, forming iron 
sulphate. This copper goes into the silver, but it is very small 
in quantity, and no attention is paid to it, as a little copper in 
the silver does no harm. When the decomposition of the sul¬ 
phate is complete, the metallic silver is at the bottom of the 
tank with iron sulphate above it. The time usually required 
to finish the decomposition is from two to three hours. The fine 
silver is then drawn to the high side, v; of the vat. The iron 
sulphate solution is drawn off with a lead syphon, Fig. 5, into 
the launder, g y which connects with the vat, R, sunk below the 
level of the floor. To be sure that no particles of silver are car¬ 
ried off by the suction, a cloth is tied over the mouth of the fun- 
nel-shaped end syphon, which is twice the diameter of the tube, 
and this is inserted in a lead saucer, Fig. 6, in which there are 
six holes, which is placed on the bottom of the tank, H. By 
this means but little of the silver is carried over. 

The tank, K , was originally intended for the same purpose 
as H, but as in all ordinary times a single vat is all that is re¬ 
quired to treat the silver sulphate, it is now used exclusively to 
collect all the wash liquors containing gold and silver. After 
they have remained there sufficiently long to become settled, 
they are used in H or B, as occasion may require. The set¬ 
tlings in K, when they have accumulated sufficiently, are re¬ 
duced with iron and are added to the silver in the tank, //, 

3. Purifying the Silver and Melting it into Ingots. 

The silver remains on the high side of the vat at v, in the 
shape of a grayish powder. It is first washed with hot water to 
remove any iron sulphate adhering to it and then treated on a 
filter M y Fig. 7, made of two basins, one inside of the other. 
The lower one is made of copper, and is filled with holes; over 
the bottom of this vessel a linen cloth is placed. The upper 
one, which is exactly like the lower and fits into it, is made of 


6 


lead 0.004 m • thick, and is pierced with holes 0.01 5 in, in diam¬ 
eter. These two are placed together. The under one has two 
handles by which to lift them. They are placed in a wooden 
frame over a lead-lined vessel, q. 

The washed silver from H is placed in the upper vessel and 
carefully treated with hot water from the boiler, Q, until neither 
litmus nor ferrocyanide of potassium gives any reaction with the 
wash water. All of this water is collected in the lead vessel be¬ 
low. So long as it contains any silver it is conducted by a lead- 
lined launder 0.16 in. wide and 0.15 V. deep and 3 111, long 
into the vat K When the silver is entirely sweet, it is placed in 
the hydraulic press, Fig. 8. This is arranged on the table, V. 
The press consists of a hollow circular piece in, placed on a cast 
iron table, f which moves up and down on a piston. The circular 
piece, in, is lowered and the silver put in it; it is then raised 
against the plunger, E ; during this time water carrying fine par¬ 
ticles of silver flows out. These are caught by a leather launder 
and conducted into a vessel placed underneath the table, where 
the silver is allowed to settle. When the compression is complete 
the circular part, in, is caught by the hook, h, which is made to slip 
under a projection made for the purpose and holds it up with 
the silver cake in it. The table, f is now let down and the pan, 
r, put upon it. It is again raised. The sides of the pan, strik¬ 
ing the cylinder, raise it up so that the silver cake drops into the 
pan below and can be removed when the table,/", is lowered. The 
cake of silver is cylindrical and about 0.12 high. It is broken 
up with a chisel and hammer. The silver still contains some 
moisture. In order to remove it, it is heated to redness in a 
round retort, U, Plate 1, which connects with a sheet iron chim¬ 
ney, it, 1.8 in. high. The metal is then melted with a small 
quantity of nitre to prevent sprouting on cooling in graphite cru¬ 
cibles, Fig. 13 a. 0.38 111. in diameter, 0.5 in. high, and holding 
between four and five hundred kilos, in a shaft furnace with 
two tuyeres, V. It is poured into cast-iron molds, Fig. 11, 
which are heated, and protected with a cast-iron cover and are 
placed on the heated cast-iron plate, X, next the furnace. The 
silver is 995 to 996 fine. The ingots weigh about 75 kilos 
each and are sold in this shape, their weight, fineness and value 
being stamped on them. 


7 


4. Treatment of the Sulphuric Liquors. 

The liquid iron sulphate from the vat, H, passes from the 
launder, g, to the trough, k, in which there are eight compart¬ 
ments so divided that the liquid overflows from one to the other 
in order to facilitate the settling of the silver. The last one of 
these compartments is filled with grains of metallic lead. This 
compartment overflows into the large reservoir, R. From here 
it is raised by means of the steam injector,/, into the lead lined 
vat, D. Here it is boiled with steam. If on trial the liquor is 
found to be very acid, it is saturated with the thin iron plates, 
the same which are used in the vat, H, to precipitate the silver. 
When the evaporation has concentrated the liquor sufficiently, it 
is transferred to the two lead lined vats, N. The green vitriol 
crystallizes out on the sides on cooling. These crystals are re¬ 
moved and placed in the wooden vat lined with lead, S, to drain. 
The mother liquor which is still attached to them runs into the 
launder, d, and is carried back to the tank, R. The crystals are 
selected by their size for sale, being mixed with those that are 
produced at Goslar. Those which are too small to be sold are 
either recrystallized or are kept at the works and are used to pre¬ 
cipitate the gold. When the crystals have been removed from N, 
the contents of the vats are allowed to run to waste. Extremely 
small quantities of silver remain in the iron solution. The small 
quantities of it and of the copper sometimes used to precipitate 
the last traces of silver and which is thrown down by the iron, are 
collected either in the tanks, N, or the steam vat, D. All of these 
settlings are collected together on the lead floor, g, beside the 
crystallization tanks, and are added to the charge of ores, which 
are smelted in the other parts of the works. 

5. Purifying tpie Gold and Melting it into Ingots.. 

All the material insoluble in sulphuric acid settles at the bot¬ 
tom of the solution pot, A. It is generally allowed to remain 
there for two charges only; sometimes, however, the residues of 
four charges are allowed to accumulate. The residue, which is 
gold, and any other insoluble substances, will then weigh from 
6.5 to 7 kilos. It is boiled with fresh acid at 66° B. It is then 
allowed to cool and is transferred in cylindrical copper vessels to 
the lead-lined vat, T } Fig. 9, which is about 1 in. square and 
0.50 in. deep, where it is boiled with steam introduced into it by 


8 


pipe a , in order to separate any remaining traces of the lead^ 
or silver sulphates and of the salts of iron and copper insoluble 
in concentrated acids. In order to prevent any loss of gold 
from spilling, in the transfer, a sheet of lead is put under the 
vessel used to transfer it. It is boiled until the gold is red and 
looks very much like ground, burned coffee. At first it was 
washed several times with hot water taken from the boiler, Q,. 
but the steam does the work much better. 

The liquor from the vat, T y is transferred by means of a glass 
syphon into a porcelain vessel, where it remains sufficiently long 
to allow the gold particles which are exceedingly fine, to settle, 
and is then poured into the vat, K. In order to be sure of the 
separation of any silver which may still remain in the gold in 
the vat, T, the gold is put into a porcelain vessel where it is 
covered with sulphuric acid at 66° B, and placed in the boiler, P y 
where it is heated and then allowed to cool. This is repeated sev¬ 
eral times. When no reaction for silver is detected, the gold is 
sweetened. The liquor is then transferred. The same arrangement 
is made to catch the gold in case of a crack in the boiler, as is 
made in the case of A and B. All the acid which is volatilized 
is carried into the chimney by the opening, i. All the acid used, 
as it contains some very finely-divided gold, is kept to be used 
in the solution of the silver. 

The gold is about 920 fine. As it is not entirely fine, it is 
put into the covered porcelain vessels, Fig. 10, a, and treated on 
the sand-bath with aqua regia. It dissolves very slowly, as the 
vessel is only slightly heated. The gold contains a little graphite 
from the pots and a little silver. The silver is precipitated by 
the chlorine of the aqua regia. It contains some gold which is 
separated by several boilings With nitre. It is decomposed by 
iron to which some sulphuric acid is added. The silver obtained 
after it is sweetened is melted in a crucible and added to the 
silver in the pot, A. 

The geld goes into solution according to the following for¬ 
mula : 

Au+HN 0 3 + 3 HCl=Au CI3+NO + 2H2O 

The silver chloride is allowed time to settle and the liquid is 
drawn off with a glass syphon into a porcelain vessel, Fig. 10, b. 

It is again allowed to settle and is again drawn back into the 


APPARATUS USED IN 

PARTING GOLD 

AT 

LAUTENTIIAL 


Fig- 1 - 


Parting pot 





4lfcl 

Precipitation vats 




<3 




f —0.34—1 

& ]h Ifiin- 

Fig. 4 . 

<=,l I 1 IIP- 




Sweetening vat 


Gold purifying vat 


Mould for the Gold 


Crucible 



T 



i 

1 

g 

Fig. 9 . 


o 

T 


1. 




I 





Fig. 12 . 



Hydraulic press ^ p 


Lead Saucer, Fig. 6. 





Mould for the Silver 



Fig. 11 . 




Fig. 13 . 


SCALES OF METERS 



l Meter X> for Fig’s 10,ll',12,13,b,c, 



1 Meter3^ 6 for Fig’s 5,6,8, 


























































































































































































































































































































































9 


first vessel and so on until it is entirely clear. The residues are 
placed on a filter and washed with aqua regia. The clear liquid 
is, if necessary, concentrated under a hood with a very gentle 
heat and the gold precipitated with iron sulphate. The reaction 
which takes place is represented by the formula: 

2 AuCl3T6FeS04=2 Au~hFe2 Clod - 2Fe2(S04)3. 

Where no more gold remains in solution an excess of the iron 
sulphate causes a considerable evolution of gas from the de¬ 
composition of the nitric acid. The liquid is decanted and 
clarified in a porcelain vessel, I, Fig. 13, c' when all the gold is 
separated, it is thrown away. The gold is repeatedly washed 
with hot water. When ammonia no longer gives a reaction for 
iron it is dried on the sand-bath and melted down in Hessian 
crucibles, Fig 13, b., in the two tuyer furnace, W } under a 
cover of potash and flour, to pieces weighing about *4 kilo. 
These are melted in the same furnace in a graphite cru¬ 
cible, Fig. 13, c, and cast in a warmed iron mold, Fig. 12, 
which has been smeared with oil, into bars weighing 4 to 5 kilos 
and sold. The gold is 999.5 fine. 

All the crucibles are used several times except the Hessian. 
These are broken to get the gold out. All the old and broken 
crucibles, silver slags and rich residues are collected in the vats, 
z and Z. When a sufficient quantity has accumulated they are 
stamped, washed, fluxed, and the metal added to the cupel 
when a cupellation is made. 

Cost of the Process. 

The figures given below, which are taken without alteration 
of the amounts from Mr. B. Rosing’s paper, give a clear insight 
into the working of the process. 

Bullion Treated in 1876. 

From the Lautenthal works. 994.500 kilos. 

Bought from the Altenau works. 5,367.000 “ 

Bought from the St. Andreasberg works. 5,121.500 “ 

Coins purchased. .225 


Total 


11,483,225 kilos 








io 


Gold and Silver Produced in 1876. 


Gold in bars. 83.184 kilos. 

Silver in bars. 1,130.861 

Not accounted for in the residue. 9 I - 43 I 


Total. 11,483.225 

Iron sulphate produced. 24,300 kilos. 


The process shows a gain in gold and a loss in silver as fol- 
1 ows: 


Amount of Metal Calculated. 

Fine Gold. 

Kilos. 

Fine Silver. 

Kilos. 

In the 994.5 kilos of silver-gold from Lautenthal.. 

26.2850 

979-9415 

In the 5,367 kilos “ “ Altenau. . . . 

25.56645 

5,304.303 

In the 5,121.5 kilos “ “ St. Andreasberg 

51.99685 

5,026.7725 

In the 0,225 °f coin. 

0.00035 

0.169 

Total. 

80.19215 

11,311.186 


Actual Product. 

Fine Gold. 

Kilos. 

Fine Silver. 

Kilos. 

ii,so8 .6 i kilos stamped silver bars. 


11,282.352 

83.184. kilos gold bars. 

83.0765 

0.2820 

In the residues. 

23.500 

Total. 

83-3585 

11,305.852 


Gain in Gold. 3.16635 

Loss in Silver. 5-334 

In percentages the product was : 

Gold. 103.948 

Silver. 99.952 


The cause of the very important gain in the product of gold 
is not so much the inaccuracy of the assays as the inexact 
method of making the calculations. 

There was used during the year : 


Coke. 

Coal. 

Charcoal . 

Faggots of Wood. 

Sulphuric Acid, at 66° B 

Refuse Iron. 

Copper Sulphate. 


154 Centners. 

496 

19 Cubic Meters. 
3.60 Centners. 
412.68 
70.00 
4.00 

















































There were produced per ioo kilograms of granulated silver 
parted: 

v Gold in bars . 0.72 kilos. 

Silver in bars. 98.48 “ 

Iron Sulphate. 212. “ 

There were used for the 100 kilos of granulated silver 


parted : 

Coke. 1.34 Centners. 

Coal. 4.32 ,, 

Charcoal. 0.16 ,, 

Faggots.004 ,, 

Sulphuric Acid, at 66° B..’. 3.60 ,, 

Refuse Iron.0.69 ,, 

Copper Sulphate. 0.04 ,, 


Expenses per 100 kilograms granulated silver: 



Marks. 

Pfennigs. 

Wages. 

. 14 

72 

Material. 

. 37 

86 

General Expenses. 

. 25 

32 

Total. 

. 77 

90 


The process is a very expeditious and simple one. The 
cost of the plant is not large nor are the operations so difficult 
that they may not be very quickly learned. The objections to 
it can all be avoided with a little care. It seemed at first as 
though the great evolution of hydrogen gas which took place 
when the iron was added to the silver sulphate when the process 
was first introduced, was a serious difficulty which could not 
readily be overcome, but this has been entirely remedied by 
bailing out the crystals from the acid so that there is but little acid 
in excess, leaving nearly all the acid to be used over again. The 
objection that was first made that the use of iron would lower 
the fineness of the metals by the introduction of foreign sub¬ 
stances, such as graphite, silicon, phosphorus, &c., in the silver, 
does not hold good, for in the first place, but little foreign ma¬ 
terial is contained in an iron so very pure as the sheet iron 
used, and if they were there even in much greater quantity than 
now, it would make but very little difference, as they go into the 
slag when the silver is melted, or are burned, so that the metal 
is even purer than it otherwise would have been if copper had 
been used, as it generally is, while the iron is much cheaper. 


















I 2 


The use of the acids which have already acted once, to bring 
down the gravity of the fresh acid is also a very great advantage 
in the process. The gold is also finer from the treatment with 
aqua regia, and precipitation with iron chloride. All the plat¬ 
inum, and other platinum metals can be separated from the 
solution in aqua regia and saved. 











V 


* 







